Properties of He-rich stars. I. Their evolutionary state and helium abundance.

Details Properties of He-rich stars. I. Their evolutionary state and helium abundance. Properties of He-rich stars. I. Their evolutionary state and helium abundance.

Aug 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...324..949z&link_type=abstract

Astronomy and Astrophysics, v.324, p.949-958

Astronomy and Astrophysics

Astrophysics

15

Stars: Abundances, Stars: Atmospheres, Stars: Chemically Peculiar, Stars: Fundamental Parameters

Scientific paper

A determination of the surface gravity and an abundance analysis of helium in a sample of 17 He-rich and 5 normal, reference stars is presented. These results are derived from low resolution CCD spectra, but each star was measured at least 6 times in order to obtain a significant average spectrum for the spectroscopic variables. The helium abundances derived from the models used are very close to 0.1 for normal, reference stars and are larger for the others, clearly indicating the He-rich phenomenon in them. NLTE effects, errors on the microturbulence value or on the surface gravity do not influence the estimated helium abundances. Nevertheless, synthesized Geneva colours are affected by the He-rich peculiarity, especially the [U-B] index which systematically changes by -0.025 mag per 0.1 of He abundance for the coolest stars in the sample. We cannot confirm the correlation between the evolutionary state and the helium abundance reported previously (Zboril et al. 1994, International Conference on CP and Magnetic Stars.", Tatranska Lomnica, eds. J. Zverko and J. Ziznovsky, p. 105), although we used a more reliable technique of log(g) determination. All He-rich objects lie within the main sequence: their surface gravities are all inside the range 4.1

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